VISUAL CALLOSAL CONNECTIONS AND STRABISMUS

Strabismus is a condition that exists when the visual axes of the two eyes fail to intersect at the fixation point under binocular viewing c onditions. When it occurs in mammals during the critical period which corresponds to the period of maximal plasticity early in life, strabis mus is known to induce both morphological anomalies and abnormal conne ctions from the retina to the cortex; it further leads to binocular ne ural changes and to spatial vision deficits, especially at the cortica l level. After a brief review of the already known data about the cons equences of early strabismus in cats, monkeys and humans on the develo pment of the visual system and of visual perception, new data are pres ented here concerning interhemispheric connections in the cat. In norm ally-reared kittens, visual callosal transfer is shown to be almost ad ult-like as soon as 12 days after birth: it is almost limited to the 1 7/18 border of the visual cortex when using visual stimulations in spi te of the presence of still numerous juvenile exuberant callosal proje ctions. In contrast, callosal transfer of visual information is extend ed to both areas 17 and 18 after strabismus, leading to the conclusion that at least some juvenile exuberant callosal projections are not on ly anatomically but also functionally stabilized after such an oculomo tor disease. The possibility that similar abnormalities might be prese nt in monkeys and humans is discussed.